It is well known that organoalkoxysilanes are useful as water-repellent agents for porous inorganic base materials, i.e., construction materials such as concrete, mortar, and masonry. Such water-repellent agents are normally used in the form of organic solutions prepared by dissolving organoalkoxysilanes in organic solvents. However, the organic solvents used for the above purposes are toxic and easily flammable. Furthermore, since they raise a question of environmental pollution, a need exists for water-repellent agents in the form of water-based emulsions prepared by emulsifying organoalkoxysilanes with the use of water as a diluent.
It has been proposed to use water-repellent agents in the form of emulsion compositions prepared by emulsifying an alkylalkoxysilane with the use of nonionic surfactants having a HYDROPHILE-LIPOPHILE BALANCE (HLB) within the range of 4 to 15. In this regard, reference may be had to Japanese Examined Patent Application (Kokoku) HEI 3-13195/U.S. Pat. No. 4,648,904 issued Mar. 10, 1987. For emulsion compositions prepared by emulsifying an alkylalkoxysilane with the combined use of both nonionic surfactants and anionic surfactants, reference may be had to Japanese Unexamined Patent Application (Kokai) HEI 4-114979.
However, since the alkylalkoxysilane and water are separated from each other over time, the aforementioned compositions are inferior to the organic-solvent type water-repellent agents with regard to their storage properties. Furthermore, when they are applied onto the surfaces of porous inorganic base materials, they cannot impart sufficient water-repellent properties to these surfaces.
It was proposed, therefore, to solve these problems by means of an emulsion composition prepared by emulsifying an organoalkoxysilane and an organopolysiloxane of a specific structure with the use of an anionic emulsifier. In this regard, reference may be had to Japanese Unexamined Patent Application (Kokai) HEI 6-313167. However, this emulsion composition required a significant drying time until the coated surface could reach sufficient water-repellent properties. In addition, the obtained water-repellent properties quickly deteriorated.